In prior art nonvolatile semiconductor memory devices, a wordline voltage is applied to a wordline of a selected memory cell in order to program the selected cell. The wordline voltage has a voltage level higher than the circuit's external voltage. An internal wordline voltage generator circuit is used to generate the wordline voltage from an external voltage source.
FIG. 1 is a schematic diagram illustrating a conventional wordline voltage generator for a nonvolatile semiconductor memory device. The wordline voltage generator typically includes a wordline voltage pump 20 activated in response to a pumping enable signal VPPEN. The pumping enable signal VPPEN is generated by a pumping enable signal generator 30 which is activated by a program command signal PCOMM for a selected memory cell. The wordline voltage pump 20 raises the wordline voltage VPI to a target voltage by stepping up a power source voltage VCC. Conventionally, the power source voltage VCC is about 1.8 V and the target voltage of the wordline voltage VPI can be up to about 10 V.
A conventional wordline voltage generator is designed to raise the wordline voltage VPI by a pumping operation through the wordline voltage pump 20. As a result, in a conventional wordline voltage generator a considerable amount of time is required to reach the target voltage VPI after activation of the pumping enable signal VPPEN. In modes requiring a high speed programming operation, the time required to reach the target voltage of the wordline voltage VPI may causes a problem by degrading the overall operating speed of the device.